Nowadays, ultrasonic motors, also known as piezoelectric motors, and other piezoelectric actuators are commonly used in conventional cameras, digital cameras and camera phones, that are functioned as the drives of optical lenses for focusing the same and are becoming one of the most important elements for optical products. One such example is the Helimorph® piezoelectric actuator of 1 Ltd., England. It is a coil-like bimorph piezoelectric ceramic actuator. The actuators have some properties of compact, low power consumption, silent operation and high displacement to act as the mechanism for focussing. However, while manufacturing the coil-like Helimorph® piezoelectric actuator from a raw bimorph piezoelectric ceramic, a great amount of procedures are required to be accomplished manually, that are not preferred to be done by automatic machinery since the referring manufacturing procedures are difficult and highly delicate that manual operation can reduce the risk of low yield and instable quality. As the manufacturing of the coil-like bimorph piezoelectric ceramic actuator requires many man powers, it is difficult to apply the aforesaid coil-like piezoelectric actuator massively in industries relating to conventional cameras, digital cameras and camera phones.
Moreover, it is highly common and had already a prior art for a conventional camera to adopt piezoelectric motors or other piezoelectric actuators in its configuration. Such applications can be seen in U.S. Pat. No. 4,755,705, U.S. Pat. No. 4,786,836, U.S. Pat. No. 4,829,209, U.S. Pat. No. 4,935,659, U.S. Pat. No. 4,952,834, U.S. Pat. No. 4,959,580, U.S. Pat. No. 5,013,982, and so on. As the sizes of those conventional film-using cameras are usually large enough, they will have no problem accommodating the prior-art piezoelectric motors within their configurations. Nevertheless, as digital cameras are gradually replacing the conventional film-using cameras and cellular phones with auto-focus camera are becoming more and more popular, the aforesaid prior-art piezoelectric motors are becoming too bulky and no longer suitable to fit in those two products since the sizes of the two are usually smaller that that of a conventional camera. Hence, it is noted that the size of the prior-art optical lens module is the major restriction preventing the miniaturization of digital camera and camera phone.
There are already a few patents, dissertations and researches relating to the development of compact piezoelectric-driving optical lens for digital cameras and camera phones. However, the structures of all those compact piezoelectric-driving optical lens are too complicated to be manufactured in batch processes.
Please refer to FIG. 1, which is an exploded perspective view of an piezoelectric lens assembly, disclosed in U.S. Pat. No. 6,710,950, entitled “Piezoelectric actuator for digital camera optical system”. The lens assembly, as shown in FIG. 1, consists of a support tube 9 and a lens tube 10. Lens tube 10 holds the lens and is mounted coaxially within support tube 9 while being supported within the support tube 9 for movement in an axial direction. The circuit board for the piezoelectric drive is a flexible printed circuit board 14 arranged about the outer cylindrical surface 15 of the support tube 9. A plurality of piezoelectric elements, as the piezoelectric element 11 illustrated in FIG. 1, and their associated components are connected and supported directly by the flexible circuit board 14. The assembly of flexible circuit board and a resilient insulating sheet 15 is held in place on support tube 9 by a split ring shaped spring 16. Support and motion for the lens tube 10 is provided by the plural piezoelectric elements. However, the autofocus capability of the lens assembly is entirely dependent on the displacement of the lens tube 10, and consequently, it is bulky and difficult to provide an accurate circuit control.
Please refer to FIG. 2, which is a perspective view of a lens driving device, disclosed in U.S. Pat. No. 6,853,507, entitled “Lens driving device”. The cylindrical stationary barrel 7 is mounted on the base 35 while the cylindrical rotary barrel 6, also mounted on the base 35, is disposed surrounding the stationary barrel 7. The focus lens 1, fitted in a lens frame 3, is movably mounted within the stationary barrel 7 in a manner that the bosses 11 thereof are projected outward. The barrels 6 and 7 are provided with the linear guide slots 6a and 7a for receiving the bosses 11 so that the lens 1 may be shift forward and backward along the guide slots 6a and 7a. Moreover, the driving member 30, also mounted on the base 35 while enabling its teeth-like segments 31 to be arranged substantially adjoining the barrel 6 so that the segments are in contact with the barrel 6. The piezoelectric actuator 10, being arranged in the form of a ring around the rotary barrel 6, is contracted or expanded radially in response to an input signal from the outside. As the piezoelectric actuator 10 repeats radial contraction toward the barrel and radial restoration from the same, the drive member 30 is driven to repeat contraction and restoration in response to radial contraction of the piezoelectric actuator 10, pushing the inclined segments 31 outward, so that the segments 31 rotate the rotary barrel 6 along the inclination of the segments 31 and thus drive the lens 1 to move axially inside the stationary barrel 7. However, the cost of the lens driving device is expensive since the structure of aforesaid lens driving device is still very complicated, not to mention the difficulty of manufacturing the driving member 30, and the piezoelectric actuator 10 must be polarized in segment.
Please refer to FIG. 3, which shows a lens driving apparatus, disclosed in Korea Pat. Appl. No. 1020040078265, entitled “Transfer unit, in which a lens and an actuator are formed in one body”. The lens driving device is substantially a cylinder 19 having a guide rod 12, a piezoelectric member 13 and a supporting block 14 arranged therein. However, as certain mass is required in the aforesaid lens driving device for causing inertial force, not only the weight of the lens driving device is increased, but also the diameter of the cylinder is increased.
As the structures of all those aforesaid prior-art piezoelectric optical lenses are very complicate, not only they are difficult to manufacture, but also they are not easy to be assembled that is especially true for the assembling of the piezoelectric stators. Hence, the driving force provided thereby is diminished. Moreover, as some minute parts thereof can not be fabricated by machine, the consumption of man-power and cost are increased. Thus, although the sizes of aforesaid prior-art piezoelectric-driving optical lenses are reduced, they have no competitive advantage over cost reduction and thus are not feasible for commercial marketing.
Therefore, it is in need of a piezoelectric-driving optical lens, which is compact, solid, simple-in-structure, ease-to-manufacture, ease-to-assemble, and capable of exerting a comparatively larger torque.